A new of brand of milk arrives at some California grocery stores this month as its makers pin their market hopes on a controversial theory that one tiny protein may be the culprit behind some people's dairy-induced tummy troubles.

The beverage is called a2 Milk — a direct nod to a single protein, called A2, now fueling scientific debate.

Pasteurized and free of growth hormones and antibiotics, a2 Milk already is filling the glasses of folks in New Zealand, Britain and Australia. It doesn't taste any different or pack any more nutritional punch than the cow's milk in your refrigerator, say its makers, the a2 Milk Company, based in New Zealand.

But the product does contain the A2 protein. And some research suggests A2 is beneficial for people who feel queasy and bloated after drinking dairy, but who aren’t truly lactose intolerant. In fact, the inclusion of that particular protein makes a2 Milk resemble, chemically speaking, the cow's milk people were drinking many centuries ago.

The company contends that it’s not lactose that gives some people dairy-related digestive issues — rather, it’s yet another protein called A1 that's typically present in store-bought milk.

1 emerged thousands of years ago due to a natural genetic mutation within European dairy herds, said Andrew Clarke, chief scientific officer at the a2 Milk Company Other mammals, including female humans (think breast milk), produce milk containing only the A2 protein.

Because that DNA mutation was associated with high-milk producing breeds, A1 spread throughout cows in Europe and the United States. Today, dairy herds in the U.S. and Europe, among others, are generally comprised of cows that carry both the A1 and A2 proteins, though some cows may be purely A1 and others purely A2.

The so-called “old world cows,” namely those in Africa and Asia, continue to produce only the A2 protein, said Clarke. All milk sold by The a2 Milk Company, which developed a DNA test, is certified as being from cows that only produce A2.

During the past two decades, there’s been some research focusing on the health effects of A1 and A2. But it's within those findings that the story starts to get a little curdled.

Some of this population-based or animal research suggests that consumption of milk with A1 is tied to the development of diabetes and heart disease, among other ills. That assertion sparked a firestorm of interest — and controversy — leading the European Food Safety Authority to release a 2009 report stating "a cause and effect relationship” between consumption of A1 and non-communicable diseases was not established.

The first peer-reviewed, double-blind, randomized human trial examining A1 versus A2 was published in the European Journal of Clinical Nutrition last year.

Researchers found those on A2 reported less bloating, less abdominal pain, and firmer stools. However, only a small portion of study's 36 participants described themselves as being intolerant to milk before the study began. Within that subgroup of eight people, researchers also were able to show differences in bloating, pain, gas and voiding difficulty, said lead author Sebely Pal of Australia’s Curtin University.

But that tiny sample size was “insufficient to show statistical significance,” or to offer conclusive proof, Pal added.

The next step in cracking this scientific riddle: a digestion study that involves recruiting more participants who self-define themselves as being intolerant to milk, Pal said.

At this point in the debate, many nutrition experts say the science is too preliminary to jump on the A2 bandwagon.

“The data (of the human trial) is equivocal and self-reported data always me nervous,” said Greg Miller, chief science officer for the National Dairy Council. “The sample size is small, and I don’t find it compelling in any way.”

“This theory (A1 vs A2) has been around a long time,” adds Madelyn Fernstrom, health and nutrition editor for NBC News and TODAY. “But there’s no real proof that one is better than the other. There needs to be a lot more work done on this."

However, that little A2 protein isn’t going to hurt you. “I’m all for milk or dairy products, except for raw ones,” Fernstrom said. “I don’t see any harm in giving it a try if you have some issue with digesting dairy. Who knows? It could potentially be easier for you to digest — or not.”

This new brand, a2 Milk, will arrive at some California grocery stores this month. Makers contend its chemical makeup, containing a protein called A2, may allow some people to again drink milk without belly-disrupting symptoms.
a2 Milk Company

While dairy has always been the darling of dietitians, U.S. consumers are drinking less milk in favor of other beverages.

But low-fat or fat-free dairy provides a lot of vital nutrients, including calcium, potassium, vitamin D, and protein. It’s this nutrient profile that too many people are missing, said registered dietitian Bonnie Johnson, a2 Milk's U.S. Nutrition Director and a 20-year veteran of the dairy industry.

“A lot of people believe they are lactose intolerant but have never been tested, and have stopped drinking milk,” Johnson said. “They may simply be having a hard time with the A1 protein and they’re missing out on some really good nutrition.”

If you are lactose intolerant or have a cow-milk allergy, a2 Milk isn’t for you. That’s because a2 Milk isn’t medicine, it’s milk, and it will sell for $4.50 per half gallon (whole, reduced fat, low fat, and fat-free) at Whole Foods and Ralphs stores in California as well as at some independent California grocers. If a2 Milk catches on, the company hopes to go nationwide.